The purpose of this study was to identify early behavioral, physical and familial characteristics of children with a significant discrepancy between intellectual ability and school achievement in the first and second grades. Low achievers, followed from the prenatal period to age 7, were compared with their IQ-matched academically successful controls on prospectively ascertained indices of cognitive and physical development and family characteristics. Cognitive deficits and behavioral deviations were found in the preschool period. Indices of socioeconomic status (SES) and family structure were more strongly related to low achievement than were indices of physical development and medical status. Low achievers were born into low SES, large families and were primarily male. As preschoolers, they had difficulties with language and relatively low IQ scores. At age 7, signs of deviant behavior, verbal and non-verbal cognitive deficits, and neurological soft signs were present. Hyperactive low achievers had an increased frequency of obstetrical complications.